Removed initialisation of low res standart poster

Poster should be set using the standart functionality of video.js.  e.g.

              myPlayer.poster(posterImage);


If a youtube standart poster is wanted, it could still be set via the API, following these naming conventions.
http://stackoverflow.com/questions/2068344/how-do-i-get-a-youtube-video-thumbnail-from-the-youtube-api